The possibility of driving LEDs directly from an AC mains voltage is known from the prior art. However, known driver modules are disadvantageous because of a flickering effect occurring when an LED string is operated. For an LED string to emit light and for a current to flow through the LED string, it is indeed necessary that the voltage across the LEDs is high enough. The voltage should be higher than the forward voltage of the LED string. Since the supply is achieved by an alternating voltage, the forward voltage necessary for emitting light is not reached during the whole period of the mains supply. This is perceived as a flickering effect.
Document WO 2011/141856 A1 provides a driver module for driving LEDs from a rectified mains voltage. The driver module comprises a current source, first and second capacitors and two diodes. In a first phase the current source is deactivated, the capacitors charge from the rising input voltage, and the LEDs are fed only by the second capacitor. In a second phase, the capacitors are charged such as no current is drawn from the mains, and the LEDs are still fed by the second capacitor. In a third phase when the input voltage drops further, both capacitors discharge and the LEDs are supplied mainly by the first capacitor.